[PATCH v3 14/20] fuse_dentry_revalidate(): use stable parent inode and name passed by caller

Al Viro
2025-01-23T01:46:46Z

No need to mess with dget_parent() for the former; for the latter we really should
not rely upon ->d_name.name remaining stable - it's a real-life UAF.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
fs/fuse/dir.c | 17 +++++++----------
1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index d9e9f26917eb..3019bc1d9f9d 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -175,9 +175,11 @@ static void fuse_lookup_init(struct fuse_conn *fc, struct fuse_args *args,
memset(outarg, 0, sizeof(struct fuse_entry_out));
args->opcode = FUSE_LOOKUP;
args->nodeid = nodeid;
- args->in_numargs = 1;
- args->in_args[0].size = name->len + 1;
+ args->in_numargs = 2;
+ args->in_args[0].size = name->len;
args->in_args[0].value = name->name;
+ args->in_args[1].size = 1;
+ args->in_args[1].value = "";
args->out_numargs = 1;
args->out_args[0].size = sizeof(struct fuse_entry_out);
args->out_args[0].value = outarg;
@@ -196,7 +198,6 @@ static int fuse_dentry_revalidate(struct inode *dir, const struct qstr *name,
struct dentry *entry, unsigned int flags)
{
struct inode *inode;
- struct dentry *parent;
struct fuse_mount *fm;
struct fuse_inode *fi;
int ret;
@@ -228,11 +229,9 @@ static int fuse_dentry_revalidate(struct inode *dir, const struct qstr *name,

attr_version = fuse_get_attr_version(fm->fc);

- parent = dget_parent(entry);
- fuse_lookup_init(fm->fc, &args, get_node_id(d_inode(parent)),
- &entry->d_name, &outarg);
+ fuse_lookup_init(fm->fc, &args, get_node_id(dir),
+ name, &outarg);
ret = fuse_simple_request(fm, &args);
- dput(parent);
/* Zero nodeid is same as -ENOENT */
if (!ret && !outarg.nodeid)
ret = -ENOENT;
@@ -266,9 +265,7 @@ static int fuse_dentry_revalidate(struct inode *dir, const struct qstr *name,
if (test_bit(FUSE_I_INIT_RDPLUS, &fi->state))
return -ECHILD;
} else if (test_and_clear_bit(FUSE_I_INIT_RDPLUS, &fi->state)) {
- parent = dget_parent(entry);
- fuse_advise_use_readdirplus(d_inode(parent));
- dput(parent);
+ fuse_advise_use_readdirplus(dir);
}
}
ret = 1;
--
2.39.5